Separators are used in batteries, in particular in lithium-ion batteries, to separate the anode from the cathode and, in particular, to prevent short circuits. Ions, in particular lithium ions, migrate from one electrode to the other during the charging and discharging of the battery cell. For this purpose, the separator is designed to be ionically conductive. Chemical reactions take place on the cathode and on the diode during the operation of the battery cell. In particular, lithium-ion storage batteries exist, which include graphite anodes, in which lithium ions migrate from the anode to the cathode through a separator during discharging and are intercalated into a transition metal oxide, for example Li1-XNi0.33Mn0.33O2. The lithium ions are intercalated into the anode during charging.
Lithium storage batteries that include metal anodes are also known, which contain, in particular, lithium. The cathode contains an organic or inorganic sulfur compound or pure sulfur. During discharging, lithium ions are chemically combined with the sulfur or the sulfur compound in the cathode, whereby polysulfides, for example, are formed. An electrolyte is situated between the electrochemically active sulfur compounds. Polysulfides, among other things, may be released thereby. The released polysulfides may accumulate on the anode and contaminate it and thereby destroy the battery cell.
It is known for separators made from organic materials, for example made from polyethylene or polypropylene, to be highly ionically conductive but also permeable to polysulfides. Separators made from inorganic materials are furthermore known, which are not permeable to polysulfides, but which have a relatively low conductivity for ions.
In the battery cell, lithium ions which are deposited onto the anode during charging may form dendrites thereon, which grow toward the cathode through the separator and trigger a short circuit upon reaching the cathode. Dendrites of this type may penetrate, in particular, separators made from organic materials.
A separator is known from U.S. Pat. No. 3,625,771, which includes a polymer mixture as well as particles of inorganic materials. Polysulfones, polyepoxides, and polyphenyl oxide, for example, are provided in the polymer mixture.
WO 00/336671 A1 describes a separator, including a microporous pseudoboehmite layer, which is in contact with a protective layer. The protective layer includes a polymer made from multiple monomers, for example acrylates, styrene or epoxide. The protective layer can also include a mixture of organic and inorganic material.
A separator for batteries is also described in WO 2006/088 959 A2. The separator contains a layer of additives, for example clay, clay minerals as well as metal sulfides.